Concern for the environment as well as increasingly stringent regulation of air quality, pollution and hazardous waste has created a need for alternatives to the use of petroleum and petroleum-based products in ink compositions. The primary focus has been on the development of water- and soy-based printing inks. The major reason for using water-based ink compositions is that because organic solvents are not present except in very small quantities, potential problems such as toxicity, flammability and other hazards are minimized. The major drawback of the currently available water-based inks, however, is their generally poor water fastness, which limits their utility.
The present invention is addressed to the aforementioned limitation in the art, and provides a water-based ink composition which is also water-fast. That is, the ink compositions are prepared in water, substantially without toxic and/or hazardous organic solvents, but after printing and drying become insoluble in water and many of the common organic solvents as well.
The novel ink compositions are advantageous in other ways as well. In contrast to many ink compositions of the prior art, the compositions of the invention may be used on a wide variety of substrates, dry quickly after application, and tend not to bleed or smear after drying. In addition, the present ink compositions are generally low in viscosity (and thus relatively easy to work with), display good soak resistance, and have a relatively long shelf life, typically on the order of a year or more.
Traditional water-based inks are based on resin systems which are dispersed in water. Several references describe inks which are based on aqueous vehicles. U.S. Pat. No. 5,106,417 to Hauser et al., for example, describes low viscosity aqueous printing ink compositions based on polyacrylic resins containing carboxyl groups, and which also contain a humectant, pigment and, optionally, a water-dilutable organic solvent. U.S. Pat. No. 5,166,245 to Zuraw et al. describes water-based printing inks made with modified rosin grinding resins. U.S. Pat. No. 5,242,489 to Schwarz, Jr., et al., describes an ink composition containing a polymeric additive in addition to a colorant and an aqueous liquid vehicle. U.S. Pat. No. 5,244,496 to Easton et al. describes a water-fast ink composition containing an amine, an acrylic emulsion resin binder, a triamine dye, and water. However, the water-based inks disclosed in these references do not provide the aforementioned advantages of the invention; primarily, these inks of the prior art are not both water soluble and water-fast.
Overview of Related Art
In addition to the publications cited in the preceding section, the following references are of interest as they relate to ink compositions based on aqueous liquid vehicles:
U.S. Pat. No. 3,951,892 to Drury et al., which describes a fountain ink composition containing an aqueous dispersion of a styrene polymer and a colorant;
U.S. Pat. No. 4,066,585 to Schepp et al., which describes solvent-free printing inks for intaglio or flexographic printing based on synthetic resins such as polyamides or polyester amides, and are solid at room temperature but used at temperatures at which the compositions melt and flow;
U.S. Pat. No. 4,155,768 to Adams et al., which describes an ink composition for use in ink jet comprising an aqueous solution of a water soluble dye in a polyamine, and having a pH of 8 or lower;
U.S. Pat. No. 4,163,675 to Hirano et al., which relates to an ink composition containing water, a water soluble dye, a naphthalene derivative which is present at about 0.1 to 10% by weight, and, optionally, a glycol or polyglycol constituent as a moisture-retaining agent;
U.S. Pat. No. 4,197,135 to Bailey et al., which describes an alkaline ink composition stated to be water-fast and useful in ink jet printer applications, wherein the composition is an aqueous solution having a pH of 8 or higher, and contains a water soluble dye and a polyamine having seven or more nitrogen atoms per molecule;
U.S. Pat. No. 4,365,035 to Zabiak, which describes a water-based ink composition having an acrylic resin, an inorganic pigment, a solvent (e.g., low boiling alcohol, or water-alcohol mixture), a basic compound dissolved in the solvent (e.g., ammonium hydroxide), and a plasticizer;
U.S. Pat. No. 4,545,818 to Inoue et al., which generally describes a water-based ink composition containing a water soluble or water-dispersible colorant, a hygroscopic wetting agent (e.g., dihydric alcohol, polyhydric alcohol, pyrrolidone or urea), xanthan gum and, optionally, an organic solvent drying agent (e.g., a glycol ether);
U.S. Pat. No. 4,756,758 to Lent et al., which describes thermochromic jet ink compositions which are formulated to contain two different dyes and having a resin such as a phenolic resin, a solvent liquid carrier system (e.g., based on a lower aliphatic alcohol and a lower aliphatic branched ketone) and, optionally, surfactants, plasticizers or the like, and wherein the compositions have a viscosity from 1.6 to 7.0 centipoises (cP) at 25.degree. C., an electrical resistivity from about 50 to 2000 ohm-cm and a sonic velocity from about 1200 to about 1300 meters/second;
U.S. Pat. No. 4,791,165 to Bearss et al., which describes a water-fast and lightfast ink composition having a hygroscopic component (e.g., glycol), water, a polymer blend and a dye;
U.S. Pat. No. 4,883,714 to Barton et al., which describes a flexographic printing ink composition containing polyester materials, polyvinyl alcohol and pigment;
U.S. Pat. No. 5,108,505 to Moffatt, which describes ink containing a cyclodextrin to solubilize a water-insoluble dye in a water-based ink;
U.S. Pat. No. 5,162,399 to Sharma et al., which describes a method for making ink millbase using a water-dispersible polyester in combination with an acrylic polymer;
U.S. Pat. No. 5,221,334 to Ma et al., which relates to a pigmented ink composition for ink jet printers wherein the composition is formed from an aqueous carrier medium and insoluble colorants dispersed in an AB or BAB block copolymer having a hydrophilic segment;
U.S. Pat. No. 5,275,646 to Marshall et al., which relates to ink-jet ink compositions which are stated to be free of volatile solvents and formulated to include a mixture of colorant, a water soluble polar conductive material and liquid phase, and, optionally, stabilizers, surfactants and wetting agents;
U.S. Pat. No. 5,288,160 to Li et al., which discloses an ink composition having a pH in the range of approximately 8 to 10, and which contains, among other components, an acrylic resin and a pigment;
U.S. Pat. No. 5,316,575 to Lent et al., which relates to jet printing ink compositions containing a resin, a colorant, and other optional components, wherein the compositions are stated to be "substantially free of volatile organic components" and, like the ink compositions in U.S. Pat. No. 4,756,758 to Lent et al. summarized above, have a viscosity from 1.6 to 7.0 centipoises at 25.degree. C., an electrical resistivity from about 50 to 2000 ohm-cm and a sonic velocity from about 1200 to about 1300 meters/second;
European Patent Publication No. 223,501, which describes a water-based ink compositions containing water and the reaction product of a water soluble polymer such as a polyethyleneimine with a reactive chromophore; and
Japan Kokai Publication No. 56147860, which describes inks containing pigments, polymer dispersing agents and 1,3-dimethyl-2-imidazolidinone in aqueous media.